You've hit some bottleneck in MongoDB. Now what do you do? How do you figure out what part of your system is causing the problem? MongoDB offers a number of tools for diagnosing performance issues and monitoring areas of your application and infrastructure that may need additional resources or attention. These include mongostat, mongotop, various parts of MMS and mtools. In this talk we will walk through a number of performance scenarios and use these tools to diagnose problems and common (and not so common) pitfalls in your MongoDB cluster.